KE7001 Biochemistry Lectures

Protein structure and function

Reading material: Stryer, chapter 3.4-6, 4.5 (Horton Chapter 4.)

Abstract: To a large extent, globular proteins are built up by ordered structures; the secondary structure elements a-helices and b-pleated sheet. These arise when the same phi/psi angles are repeated over a number of residues and are stabilised by hydrogen bonds involving the main chain carbonyl oxygen and peptide nitrogen. Secondary structural elements are joined by loops or turns, and are often combined in particular ways called motifs that in turn are combined to generate functional protein domains. A single polypeptide chain may fold as a single or as several domains. It is not uncommon that proteins consist of several polypeptide chains. In such proteins, each chain is called a subunit.

Folded proteins are formed primarily because hydrophobic side chains tend to avoid contact with water. The folded conformation is stabilised by the combination of a large number of weak interactions.

Key concepts:
Secondary structure (a-helix, b-sheet)
Turns, loops
Domains
Subunits
Water soluble proteins have hydrophobic cores
The hydrophobic effect is the main driving force for protein folding
By forming secondary structure elements, the hydrophilic main chain regions are hidden from the hydrophobic interior of the protein
Stabilizing forces
Hydrogen bonds
van der Waals forces
Ionic interactions
Disulfide bonds

Links:
Stryer: Elements of Protein Structure (Structural insight, use Netscape/Chime)
Stryer: Chapter 3 Living figures (Use Netscape/Chime)

The MIT Hypertextbook: From primary to quaternary structure
BioTech: An Introduction to Proteins

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